questionswhat's the better rechargeable battery for a…

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NiMH is better, though likely more expensive.

NiMH have higher capacity in a given size and thus will be able to keep the light on longer, provided that the sun is out long enough to adequately charge the cell. They don't (much) suffer from the memory effect, so they can be recharged even if not completely discharged with no significant loss in capacity. They don't have Cadmium, so are not as bad for the environment as NiCds (the Cd of which means Cadmium).

I'd never really thought about this before, but the on again, off again nature of sunlight on a partly cloudy day would not be good for a NiCd (as in charge, discharge, charge discharge, etc.) and likely exacerbate the natural memory effect of NiCds.

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Lithium Ion if you can get it I believe if not the above answers seems genuine.

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@straightrazor:

I can assure you that my answer above is a genuine, made in the USA answer. Whether or not it is correct might be up for debate, but it is indeed a genuine answer.

(Sorry, I'm in somewhat of a goofy mood at the moment.)

I'll agree that Li ion might work better than NiMH but they'll almost certainly be more expensive and might not recharge as well (depending on how the solar light fixture's recharging circuitry is designed).

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i believe it goes NiCd < NiMH < LiIon as far as consumer 'AA - AAAA' type batteries go. just the progression of technology.

when NiCd and NiMH were both 'popular' on the market 10-15 years ago NiCd were cheaper to produce, NiMH were 'new' and expensive.

LiIon is the mostly the standard now, waiting for the 'better/cheaper' energy density batteries. that's why one of the big money industries to go into right now, is alternative energy research, especially the next best batteries.

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I've tried all three (inadvertently) in solar rechargeable outdoor lighting. Well, more truthfully, my mother-in-law took a bunch of my batteries and fitted them into her lights, and raved about how much better they were. My first thought was 'of course it's better, the batteries you put in are worth more than the lights...'

Family issues aside, here's what we found. The batteries in the home improvement center lights were absolute trash to begin with. That they ever worked shocked me. We independently recharged them with a very good charger, and while they worked great for a couple days, it went back to trash.

NiCds worked best in incandescent lights, but only gave good light for about 2 hours after sunset. Plenty of time to get home and in the house, but no wow factor later at night. NiMH gave brighter light, but failed quicker (maybe 1.5 hours?) at full brightness with some light up to 5 hours later. LIons gave full for 1.25 hours, and dim for the rest of the night.

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If you fully drain a NiMH battery, it will no longer accept a charge. The only real drawback.

source

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@bogie21: You hit the nail on the head. If your solar light runs the batteries right down to flat, get NiCads. The memory effect doesn't apply as alleged above, but only when the charge/discharge cycle is exactly the same for a long period of time. NiCads can stand being run out of juice much better than NiMHs. Just remember to recycle them or dispose of them as toxic waste. If, OTOH, your light has a low-voltage cutoff, NiMH batteries will provide much higher capacity. (This capacity can only be used if the solar panel provides much more juice on a sunny day than the light can use that night, though.)

Since your light won't say whether or not it has a low voltage cutoff, you'd have to wait until it went out, pull the batteries, and then measure their voltage to find out.

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Most modern devices made to charge batteries while they are installed in said devices incorperate PCBs Prtection Circuit Boards to keep the batteries from draining past the point where they will no longer take a charge.

Just wanted to point that out so people are not afraid of using the rechargables.

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If you are a little handy, consider a system that will work off of an small external solar panel and a 12 volt 280cca battery. Depending on the number of lights this should work for you. And the solar panel should be able to collect energy even on overcast days.